Film-surfaced panel and method for manufacturing the same



Jun 3, 1969 w. SALO ET AL 3,447,988

FILM'SURFACED PANEL AND METHOD FOR MANUFACTURING THE SAME Filed July 12, 1965 INVENTORS. HENRY VV. S'AlO Bel/6'6 H. 57710 BY WILL/AM 1?. '5'4460 m A), M

AIfTOE/V'? United States Patent U.S. Cl. 156-229 5 Claims ABSTRACT OF THE DISCLOSURE A method in which a transparent regenerated cellulose film is adhesively bonded, while in a swollen and stretched condition, to a structural panel containing natural wood.

This invention relates to a panel, the surface of which is finished by application of a film to it, and the method of manufacturing such a film-surfaced panel. Such panel may be of plywood, although it can be of other materials such as hardboard, particle board, or flakeboard, all of which may be considered to be boards made of woody material.

Finishing the surface of a panel of woody material, such as of plywood, has, in the past, presented a troublesome problem, particularly if such panel is to be used for interior or exterior decorative or finishing purposes. The surface of Douglas fir plywood, or even plywood having surface layers of other types of wood, is not particularly attractive. Even if such surfaces are attractive when the panel has been completed, such surfaces deteriorate if left in their natural condition by darkening or becoming stained. To finish such a woody panel surface by staining or painting is not an easy problem. To prevent excessive absorption of stain into the grain of the wood it has been customary to use a filler of some type on the surface first. Frequently such fillers raise the grain of the wood even if it has been sanded smooth first. I

To finish the surface of a woody panel, such as plywood, for example, it has therefore been customary first to sand the surface smooth, then to apply a filler to the surface and perhaps again sand it, a plurality of coats of filler sometimes being required. Next, stain is applied and thereafter frequently a final coat of varnish or wax is added. Even such a finished surface is not waterproof, is not particularly resistant to stains, often tends to darken and generally is not very durable.

It is the principal object of the present invention to provide a surfacing method for woody material sheets, which will provide a virtually waterproof surface which can be colored easily with a minimum quantity of color, and which will be durable.

In producing such a protective surface for a panel it is an object to utilize inexpensive material for the surface film which can be applied by mass production techniques quickly, economically and automatically.

Another object is to provide a type of surface for woody panels which can be applied to a panel which has not been sanded, or which has even an intentionally roughened surface such as one which has been sandblasted, or striated, and which will result in a smooth, though not necessarily fiat, surface.

A further object is to provide such a protective film for panel surfaces which will cover knots and pitch pockets and prevent checking, cracking and splinterin g of the panel surface, but which will not obscure the grain appearance.

Another object is to provide a film surface .for a panel which can be colored quickly and easily with a single color application, and which color will not penetrate into the grain of the wood. In such coloring technique various types of effect can be achieved including a mottled or cloudy appearance, or providing a pattern of contrasting color shades.

Particularly it is an object to provide such a filmprotected sheet surface which will have a dull, or mat, finish rather than a glossy surface, when desired.

The foregoing objects can be accomplished by bonding to the surface of a Woody panel a sheet of basic cellophane film with a clear water-resistant, and preferably Waterproof, binder settable without requiring the application of sustained pressure at a high temperature. Such a film can be applied to the panel surface by the use of pressure rollers. The resulting surface can be colored easily and quickly by the application of a single coat of acid dye if the film used is basic cellophane, or if the cellophane film has been coated on one side, which is the exposed side of the film, the film-coated surface can be colored by the use of solvent dyes, or vat dyes, using metaxylene, paraxylene, or toluylene, as a solvent, for example.

The single figure of the drawing is a top perspective of pressure roller type, film-applying mechanism.

The present invention is most concerned with panels of woody material such as plywood, particle board, flakeboard, or hardboard, but it might be desirable to use the technique developed for other types of panels such as panels made of very inexpensive plastic, or laminated paper. Also, the technique can be applied to sawn lumber 0r peeled or sliced veneer, as distinguished from plywood made of laminated veneer sheets. The most important application of the invention is for covering a natural wood surface because of the protection afforded to such a surface, while at the same time the pleasing appearance of the grain in the wood is preserved. A typical and very important application of the invention is for providing prefinished faces for doors, the sides of which are made of plywood which may, for example, have a face of Philippine mahogany.

Of the various types of plastic film available, basic cellophane film is the most suitable for use in the present invention. In order to provide sulficient bond between the panel surface and the film the surface of the film neXt to the panel should be water-absorptive. Also, the filmcoated surface of the panel can be colored more readily if the outer surface of the film, to which the dye is applied, is likewise water-absorptive. Basic cellophane has these attributes.

A principal use of cellophane is for packaging purposes, but at least one side of such cellophane film is coated with waterproof material and usually both sides of the film are thus coated. Such coatings increase the glossy appearance of the cellophane and even the uncoated cellophane is glossy. The technique for manufacturing cellophane is described generally in articles appearing in the periodical Paper Film and Foil Converter for April and May 1960. Cellophane is made from cellulose Wood pulp, which essentially is insoluble in most of the ordinary solvents. It is converted into a soluble state by steeping the pulp in caustic soda, shredding and aging the alkali cellulose, and reacting it with carbon bisulphide to form cellulose xanthate in alkali liquor. The viscose is then aged and filtered before it is spun, or cast, into sheet form and the viscose is regenerated to cellulose in the form of cellophane.

In the manufacture of the cellophane film, after the viscose solution has passed through the slit in the casting machine and enters the sulphuric acid bath it instantly begins to harden into cellophane. In subsequent finishing stages in the casting machine the cellulose is regenerated, washed, de-sulphurized, washed again, bleached, again washed, softened and then dried by passing it around heated rolls, after which it is accumulated on a mill roll.

The bleaching operation is primarily responsible for reducing the transparency and sheen of the basic cellophane. By modifying the bleaching technique the resulting basic cellophane film can be made with a dull or mat finish, and of somewhat cloudy appearance, which is the type of film preferred for most applications of the present invention.

As the cellophane film is formed and rolled in the manner described, such basic cellophane is not waterproof. Customarily it is then coated on one or both sides to provide the amount of moisture protection desiredlow, intermediate or high, for packaging purposes. Moreover, such waterproof coatings can be applied to one or both sides of the film. For use in accordance with the present invention, however, at least one side of the film must remain uncoated so that the adhesive by which it is bonded to the panel surface will adhere firmly to the cellophane to form a secure bond. Also, it is preferable for the outer side of the film to remain uncoated if the panel surface is to be colored with water-soluble dye. Some dyes can be used reasonably effectively for coloring such a film-surfaced panel even if the outer side of the cellophane film has been coated.

The primary requirement for the adhesive is that it be capable of bonding the cellophane film tightly and permanently to the panel surface so that it cannot be peeled olr. For economy in manufacture it is also im portant that the adhesive be capable of setting without being subjected to sustained application of heat and pressure. Use of such an adhesive will enable the cellophane film to be applied to the panel surface by the action of pressure rollers. It is highly desirable for the resulting bond to be water-resistant and, for some purposes, it should be waterproof. Since an important feature of the invention is to preserve the visibility of the wood grain. in its natural appearance, the adhesive should be clear and virtually colorless, although in some applications it may be desirable to color the adhesive intentionally to provide a permanent color effect. If the film-coated surface is to be dyed subsequently the adhesive should be capable of filling the grain of the wood and serving as a barrier to prevent penetration of the dye passing through the cellophane into the grain of the wood. Moreover, an adhesive having such characteristics should be as inexpensive as possible.

The types of adhesive having the above characteristics, and which have been found to be most suitable for use in the present invention, are of the polyvinyl acetate and polyvinyl butyral types which, in this description, will be designated generally as vinyl adhesives. Such adhesives are described in the reference book entitled, Vinyl Resins, by W. Mayo Smith, published in 1958 by Reinhold Publishing Corporation of New York, Library of Congress catalog card No. 58-12825, particularly at pages 49, 51, 87 and 161 to 167. Polyvinyl butyral has good water resistance and polyvinyl acetate has moderate water resistance. Such vinyl adhesives can be combined with other adhesives such, for example, as with phenolic resin adhesives, but such a modified adhesive is still intended to be encompassed within the designation of vinyl adhesives.

If the outer side of the surfacing film is uncoated, the surface of the panel can be colored by the use of acid dyes, which are defined in Websters Third New International Dictionary at page 709. Further information is given at pages 706, 707, 708 and 710 of Websters Third New International Dictionary and in the Colour Index, second edition, compiled and published jointly by the Society of Dyers and Colourists of Great Britain and the American Association of Textile Chemists and Colorists, 1956. Acid dyes suitable for this purpose have been found to be nitro, azo, quinoline, triphenylmethane, azine and anthraquinone. One particular category of dyes which has been found to be suitable is sodium azo dyes of the monoazo, diazo, triazo and polyazo types.

If the outer surface of the cellophane film has been coated in the cellophane production process, the acid dyes which are water soluble will not penetrate the film. In that case, solvent dyes, or vat dyes, defined on page 710 of Websters Third New International Dictionary can be used in a hydrocarbon vehicle such as metaxylene, paraxylene, or toluene. A disadvantage of using cellophane coated on one surface, however, is that the resulting panel face, even if dyed, will be more or less glossy, and certainly much more glossy than when the outer surface of the film is of the uncoated type.

In manufacturing the product according to the present invention by the use of apparatus such as shown in the drawings, a roll 1 of basic cellophane is mounted in the machine from which the sheet of film passes around a guide roller 2 between adhesive applying rollers 3 and 4. Roller 4 picks up adhesive liquid from the trough 5 and applies it to one surface of the film. Such film then passes around a plurality of additional guide rollers 6, 7 and 8 before passing between the pressure or nip rollers 9 and 10. Wetting of the cellophane film by the adhesive tends to cause it to stretch. If the rollers 6 7 and '8 have convex surfaces the cellophane film will be kept stretched smoothly transversely of its length and direction of movement so that it will pass between the nip rollers 9 and 10 as a smooth sheet.

The sheets 11 of plywood or other panel material is fed into the machine by the feed rollers 12 beneath a hooded brushing roller 13. The space within the hood 14 can be evacuated by attaching to it a suction pipe 15 so that the surface of the panel to which the cellophane film is to be applied is brushed clean and the dust and dirt loosened by the brush is removed by the suction hood.

The adhesive is supplied to the trough 5 from the reservoir 16 and the flow of the adhesive to the trough through pipe 17 is regulated by valves 18. The speed of flow through the pipes 17 will be coordinated with the speed of travel of the cellophane film between the rollers 3 and 4, and the amount of adhesive which it is desired to deposit on the film. Also, the film movement will be coordinated with the speed at which the panel is fed by feed rollers 12, so that the film will simply be laid onto the upper surface of the panels as such film and panels pass between the nip rollers 9 and 10. The adhesive should be of a character such that by the time it has traveled on the film surface from the rollers 3 and 4 to the nip rollers 9 and 10, it will have become sufficiently tacky so that the pressure of the nip rolls will cause the film to adhere to the surface of the panel.

The film-covered panel 11' will then be transported by a suitable conveyor through a hood 19 to which hot air is supplied through a duct 20 for the purpose of expediting the setting of the adhesive. During its passage through this hood the edge portions of the film-surfaced panel can be gripped by short rollers 21 to assist in transport of the panel. The hood may be 30 feet long and the air may be as hot as 300 F. Upon discharge from the hood the adhesive will be set sufliciently so that the panel can be cut to length and the cut sections stacked until curing of the adhesive has been completed.

As has been mentioned, it is important for the finished surfacing of the panel to be transparent, so that a woodgrained surface beneath the film overlay will be clearly visible. Such wood-grained surface may be of natural wood grain, such as on lumber, veneer or plywood, or may be simulated wood grain such as produced photographically on a plastic backing. In either case, when the film has been applied both the adhesive and the film should be highly transparent and colorless unless the adhesive has been colored intentionally. The vinyl adhesives mentioned above have this capability, as does basic cellophane film. In order to provide a mat finish, instead of a glossy finish, the cellophane film may be somewhat cloudy before its application to the panel surface, but after the adhesive has cured the film is very transparent.

In its liquid form the vinyl adhesive is white, so that when it is applied to the cloudy film and such film is then applied to the panel surface by the nip rollers 9 and 10, the film-covered surface of the panel will initially appear white. As the curing of the adhesive progresses, however, the opacity of the adhesive and film gives way to a clear, transparent effect. Setting of the adhesive in a hot atmosphere between 200 F. and 300 F. can produce such transparent appearance and bond the film to the panel sufficiently to enable it to be cut into proper lengths in approximately one minute. A preferred temperature for the curing atmosphere is 225 F.

Instead of applying the adhesive to the film and then laying the adhesive-carrying film onto the panel, the adhesive can be applied to the upper surface of a panel being transported to the pressure rollers 9 and 10. For this purpose a roller-type glue spreader, similar to that used for applying adhesive to veneer for manufacture into plywood, can be used. In that event the dry film would be fed from the mill roll 1 around suitable guide rollers into the nip between the pressure rollers 9 and 10 where it would be pressed onto the adhesive-bearing side of the panel. Whether the adhesive is placed on the film, or on the panel, it will be evident that the spacing between the nip rollers 9 and 10 should be adjusted properly, depending upon the thickness of the panel to which the film is being applied. Also, the character of the roller 9 selected will depend upon the surface of the panel, but in any case it is preferred that the surface of such roller be somewhat resilient.

If the surface of the panel 11 is reasonably smooth, the surface of the upper roller 9 should be comparatively hard, although it should still be somewhat resilient, such as being made of rubber having a durometer hardness of approximately 80. Such film can be applied to the surface of peeled veneer which has been dried, but not sanded, and if it is desired for the resulting panel to have an even surface, the surface of the roller should have a hardness of approximately 80, or even harder. The same technique can be utilized to apply a film to the surface of a panel which has been sandblasted, or eroded with a wire brush, to remove more of the softer summer growth than of the harder winter growth of the grain. The winter growth portion of the grain will then stand out in relief. Alternatively, the surface of a panel can actually be striated by machine grooving. For applying the veneer film to such uneven surfaces the upper roller 9 should have a softer surface such as would be provided by using rubber having a durometer value of approximately 70.

As has been mentioned above, the length of the hood 19, into which heated air is supplied, can be approximately 30 feet. As also mentioned above, it is preferred that the film-covered panel be subjected initially to the effect of a heated atmosphere for approximately one minute. Thus, if the hood 19 is 30 feet long the speed of travel of the panel 11' through the hood should be approximately 30 feet per minute. This hood might be as much as 100 feet in length so that the speed of travel of the film-covered panel could then be as much as 100 feet per minute. In determining the possible speed of travel the critical factor is to make sure that the adhesive is sufficiently tacky at the time the film and the panel pass between the pressure rollers 9 and 10, and that the pressure exerted by such rollers is suificient, so that the film is pressed smoothly into contiguous contact with the surface of the panel and remains in such contact as the filmcovered panel moves out from between such rollers. After the finished panel has been cut into sections of desired length they can be stacked for a period of from one to twenty-four hours in order to complete the curing of the adhesive.

After the cellophane film has thus been applied to the panel surface and it has cured sufiiciently, the film-covered surface can be colored with dye. Such dye can be applied in various ways such as with a brush, a roller, a sponge, or a spray. The dye may, for example, simply be rubbed on or daubed on with a sponge, allowed to remain for a few seconds, such as 2 to 10 seconds, depending upon the intensity of color desired, and then the residue wiped off. Blends of different dyes can be used by successive applications. The adhesive will serve as a barrier to prevent dye penetrating through the cellophane from impregnating the grain of the wood. If desired, a wax coating can be applied over the colored film to deter moisture penetration farther.

A specialty wall panel product of attractive character can be produced by grooving the surface of the filmsurfaced panel, after the adhesive has cured, to a depth below the glue line, so as to expose some of the wood. Suitable saws, or planing cutters, can be used for this purpose. If the panel is plywood it is preferred that the depth of the grooves be less than the thickness of the face veneer. If color is applied to such grooved surface it will be absorbed to a greater extent by the wood in the grooves than it is by the surface of the panel covered by the film. Thus, the panel will have ribbons of more intense color relieving the color of the film-covered portions of the panel.

We claim as our invention:

1. A method of making film-surfaced structural panels containing natural wood at least along one side thereof including the steps of applying to an uncoated side of a dry, transparent regenerated cellulose film a liquid vinyl adhesive, prior to any contact with the adhesive coated side of the regenerated cellulose film permitting the film to assume liquid from the applied adhesive whereby the film swells and the applied adhesive becomes tacky, stretching the liquid containing film in one direction, while the film is in its stretched condition contacting the adhesive coated side thereof under pressure against the one side of a structural panel containing natural wood, and heating the combined film and structural panel without any sustained application of pressure to set the adhesive.

2. A method as defined in claim 1 wherein the regenerated cellulose film is a continuous film, and wherein such film is stretched only in its transverse direction.

3. A method as defined in claim 1 further including the step of applying a water-soluble acid dye to the exposed surface of the film after it has been applied to the structural panel and the adhesive has been set.

4. A method as defined in claim 1 further including the step of applying a water-insoluble dye in a vehicle selected from the group consisting of metalyzene, perilyzene and toluene to the exposed surface of the film after it has been applied to the structural panel and the adhesive has been set.

5. A method as defined in claim 1 further including the step of incorporating a dye into the liquid adhesive prior to its application to the one side of the regenerated cellulose film.

References Cited UNITED STATES PATENTS 1,983,870 12/1934 Ostwald 161-251 2,310,272 2/1943 Adlington 156-229 2,327,963 8/ 1943 Haas 161-250 2,418,605 4/1947 Shepherd et al. 84 2,471,497 5/1949 Roberts et al. 161-249 3,081,212 3/ 1963 Taylor et al. 156-229 3,230,126 1/ 1966 Craver 156-244 MORRIS SUSSMAN, Primary Examiner.

US. Cl. X.R. 

